Cancer remains the leading cause of death with a disproportionate toll on minority communities. Most common cancers are refractory to traditional treatments. With recent appreciation of cancer immunosurveillance mechanisms, our long-term objective is to elucidate immune mechanisms of cancer regression and to develop immunotherapy approaches that can specifically eliminate malignant cells and provide durable benefits in cancer patients. Recent studies in various pathophysiological models of immune rejection, including cancer, suggest an indispensable co-operativity in adaptive and innate immune effector cells. Our work in a mastocytoma model demonstrated that CD8+ T cells provided a necessary help to dormant natural killer (NK) cells in eliciting their antitumor function. This co-operativity of T cell and NK cell effector mechanisms led to complete tumor regression, by preventing the development of antigen-deficient tumor escape variants. A similar role of combined CD8+ T cells and NK cells was also observed by us in the rejection of mouse renal cell carcinoma Renca and by others in the control of mammary, bladder and intraperitoneal mesenchymal tumors. This signifies the importance of functional co-operativity of NK cells and T cells in tumor rejection. However, this protective team-work of T cells and NK cells fails in conditions of immunosuppressive chronic inflammation intrinsic to aggressive tumors as shown in inducible tumor models. Thus, it is imperative to investigate novel combinatorial therapeutic strategies and their mechanistic cross-talk to reduce tumor burden and potentiate anti-tumor immune effector functions by overriding tumor-induced immunosuppression. Based on our preliminary data, we hypothesize that combining tumor cell-death sensitizing bortezomib administration with adoptive NK cell transfer and immunostimulatory Notch activation should strengthen anti-tumor immune effector functions by modulating negative immune-regulatory circuits. This combinatorial strategy should overcome immunosuppressive effects of the chronic inflammation in tumor microenvironment and enhance therapeutic benefits against cancer. To test our hypothesis, we propose to address the following specific aims: Aim 1: Characterize the impact of bortezomib administration on tumor-infiltrating lymphoid and myeloid cells and their cytokine and chemokine production in the tumor microenvironment. Aim 2: Assess the effects of bortezomib on NK cell effector responses. Aim 3: Optimize NK cell adoptive therapy in combination with bortezomib and clustered multivalent DLL1 treatments in an established tumor. This proposal will be the first attempt at attacking the underexplored area of how anti-tumor functional co-operativity between the tumor- specific T cells and NK cells can be enhanced in the context of molecular targeting based on proteasome inhibition and immunostimulatory Notch signaling. The results will provide new insights for designing effective immunotherapy protocols relevant to cancers refractory to most conventional treatments and will have implications for pathophysiological conditions beyond cancer.